Presently, telephone networks have come into use, which provide so-called intelligent network (IN) functions. One such intelligent network function is the possibility of so-called virtual subscriptions. This will be explained in connection with FIG. 3 FIG. 3 schematically shows a network 1 and physical or real subscriptions 2, which correspond to subscribers. Physical or real subscriptions are associated with a physical or logical line to the network. In other words, the physical or real subscription is associated with a predetermined access point to the network, be it a physical line as in a PSTN or be it a logical access point as in a mobile telephone system. As already mentioned, each such access-based subscription is directly associated with a subscriber.
Beyond this well-known arrangement that consists of physical subscriptions and a network for routing calls between these physical subscriptions, intelligent network functions provide new possibilities, such as virtual subscriptions, in which a subscriber has a subscription that is not associated with an access, however said subscription appears to the other subscriptions like a physical or real subscription.
This is accomplished by providing processing means in switch nodes of the network, which react to specific triggering methods in calls. Such triggering methods may use numbers that are placed in front of regular calling numbers, i.e. similar to the form of an area code. When the component in a switching node that is responsible for recognizing specific triggering numbers detects such a number, a predetermined process is initiated, e.g. contacting a specific entity that handles the service functions in the network. This specific entity may then invoke the service corresponding to the detected triggering number and perform corresponding actions. Other triggering methods may use the calling party number or the incoming route the call takes to the switch.
With respect to the above-mentioned virtual subscriptions, one may distinguish between dialable and non-dialable subscriptions, as indicated in FIG. 4a and FIG. 4b. FIG. 4a schematically represents a non-dialable virtual subscription, which means that the subscription is designed for outgoing calls, i.e. can only place calls. In other words, the subscriber to this non-dialable virtual subscription may only place calls, but no one can call this subscription from the network.
FIG. 4b shows a schematic illustration of a dialable virtual subscription, which means that the subscription is only designed for incoming calls, i.e. the subscriber to this subscription may only receive calls using a number known in the public number plan.
An example for a non-dialable subscription is an account-calling-card or a credit-card-calling service, where a subscriber dials a specific access number (this action invokes the service), and then the service itself collects an account number & PIN (personal identification number) in order to authenticate the virtual subscriber, thereafter the service helps place a call for the subscriber and performs a corresponding billing operation. As can be seen, the subscriber may only use this service to place calls, but cannot receive calls from other subscribers to the network. Examples for dialable subscriptions are free-phone and premium-rate-services. It should be noted that there may also exist services that are a combination of dialable and non-dialable subscriptions, such as so-called universal personal telecommunication (UPT), in which a subscriber to this service may both place and receive calls through the virtual subscription.
The possibilities of intelligent network functions are not restricted to virtual subscriptions, i.e. services associated with subscribers, but also extend to operations conducted by and for the network operator. Examples of this are the use of specific calling numbers or other information in a call for gathering statistical information for the benefit of the network provider. As an example, an intelligent network operation may be triggered by a specific area code during a specific period of time during the day, such that the network provider may evaluate how many calls are directed towards that area during that given period of time.
While the above-described intelligent network services and possibilities greatly increase the performance of the network, they also make the management more complicated, because the number of possible situations in the network greatly increases.
One aspect accompanying network management is that of lawful call interception. The inclusion of call interception functions in networks is required by law in many countries, in order to enable to a state agency such as the police to lawfully intercept calls in the network under predetermined conditions. The classical call interception method is access-based, i.e. calls of a specific subscriber are intercepted by monitoring the switching node at that subscriber's access point to the network. Another interception method is number-based, i.e. specific numbers trigger an interception routine in a given switching node carrying the interception function. Another method involving IN includes that a service control function (see later description of FIG. 1) sends an indication to a service switching function, that monitoring should take place. Such interception methods are e.g. described in WO 98/36548 and WO 97/41678. WO 98/36548 describes providing a database in a network component, in which relevant telecommunication data on subscribers to be monitored are stored and can be transmitted to one or more monitoring authorities. It is also mentioned to provide monitoring profiles. WO 97/41678 describes a process for monitoring a communications line, in which the call number of a subscriber who is to be under surveillance is characterized by an indication given to an agency authorized to monitor calls, and a three-way-conference-call is set up involving the subscriber under surveillance, a second party calling or being called, and the agency authorized to monitor the calls.
EP 0 792 074 describes a method of providing a service in a switched telecommunication system and a suitable message interceptor. This document generally describes the concept of an intelligent network IN and the possibility of providing specific services that are generated under certain trigger conditions, e.g. translating a called number into a different number. EP 0 792 074 also specifically mentions the concept of automated call interception, in which call attempts from a list of subscribers are automatically intercepted.
WO 97 25828 describes a cellular telecommunications system having selectively associatable usage parameters. It discusses the possibility of providing a virtual subscription, which means that a user can select any available cellular terminal and make an outgoing call, in contrast to the conventional cellular system, in which a specific subscription is always associated with a specific terminal. The system of virtual subscriptions is created by having three separate registers, one associated with a user, one with a subscription and one with a terminal.
WO 97 42784 relates to a method and apparatus for facilitating law enforcement agency monitoring of cellular telephone calls. This document specifically addresses the problem that in some cellular systems the signaling protocols only transport two numbers in connection with the set-up of a cellular call. Often, this means that there is no identification of the calling party in the call set-up signaling information. In the event that the called party triggers a monitoring procedure by e.g. the police, this means that it is not possible to identify the caller.
In order to overcome this problem, WO 97 42784 suggests using the fact that a billing operation for the calling party takes place, and that this billing operation can be used to identify the calling party.